Substrate positioning system

ABSTRACT

A substrate positioning system is provided to facilitate the performing of certain processing on the substrate, such as ion implantation. The system comprises a linkage rotatably mounted to a base and an end effector member rotatably mounted to the linkage and configured for receiving a substrate. Through the synchronized rotation of the linkage about the base and the end effector member about the linkage, the system acts as a robotic unit to move the substrate to the desired location for performing processing thereon. In another aspect, the base is movable along an axis such that the system maintains a constant distance of travel for an ion beam incident on the substrate as the linkage and end effector member travel in a curved path.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/081,610, filed Feb. 20, 2002, entitled “SUBSTRATEPOSITIONING SYSTEM”, which claims priority to U.S. provisional patentapplication serial No. 60/270,644, filed Feb. 20, 2001, entitled “ROBUSTMECHANICAL SCAN ROBOT FOR AN ION IMPLANTER WITH A SINGLE ROTARYLINKAGE”, and are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to positioning mechanisms, andmore particularly, to a substrate positioning system facilitating theperforming of certain processing on the substrate, such as ionimplantation.

DESCRIPTION OF RELATED ART

[0003] Robotic units and other positioning mechanisms are known forperforming certain controlled tasks. With respect to mechanisms forassisting in ion implantation on a substrate, such as a semiconductingwafer, a mechanical scanning apparatus has been used in conjunction withion implanters to ensure that ion beams incident on the substrate reachthe whole surface area. The ion implanters typically scan the ion beamelectrically in a first axis across the substrate surface and utilizethe mechanical scanning apparatus to scan the substrate mechanicallyalong a second axis perpendicular to the first. The mechanical scan isnecessary due to the difficulty of electrically scanning the beam over alarge area of the substrate while keeping the angle of incidence of thebeam to the substrate surface constant. Additionally, the mechanicalscan must move the substrate at a certain velocity and at the correctangle of incidence as to avoid ion dosage and substrate depthnon-uniformities.

[0004] Nogami et al., in U.S. Pat. No. 5,003,183, describe a mechanismthat swings a wafer through the beam by rotating its holder from theside. Although this mechanism maintains a constant impact point of theion beam with the wafer tilted at an angle of incidence, the waferrotation must be coordinated with the scan to avoid velocity variationacross the wafer and resulting ion dosage variations.

[0005] Brune et al., in U.S. Pat. No. 5,229,615, describe a two-linkrobot arm for mechanically scanning a wafer. This device requires thecoordination of three rotary axes to maintain the angle of incidence ata constant value as the wafer is scanned, thus adding additionalcomplexity of motion.

[0006] Thus, what is desired is a substrate positioning system that canaccurately move a substrate to desired positions for performing certainprocessing thereon while having a reduced complexity of motion. In ionimplantation, the system should mechanically scan the wafer through theion beam at a constant angle of incidence while maintaining the iondosage reaching the wafer surface at relatively constant values.

SUMMARY OF THE INVENTION

[0007] It is a feature of the present invention to provide a substratepositioning system to facilitate the performing of certain processing onthe substrate, such as ion implantation. It is another feature toprovide such a system with rotatable members synchronized to form arobotic unit to efficiently and accurately move the substrate to adesired range of motion. It is yet another feature to provide such asystem with a base movable linearly along an axis such that the systemmaintains a constant distance of travel for an ion beam incident on thesubstrate as the rotatable members travel in a curved path. It is yetanother feature of the present invention to provide such a system wherethe rotatable members simultaneously rotate to maintain a substantiallyconstant incident angle of the substrate relative to the ion beam. It isyet another feature of the present invention to provide such a systemthat is easy to use, simple in operation, and particularly well suitedfor the proposed usages thereof.

[0008] The substrate positioning system of the present inventioncomprises a linkage rotatably mounted to a base and an end effectormember rotatably mounted to the linkage and configured for supporting asubstrate. Means is provided to rotate the linkage and the membersimultaneously as a robotic unit to move the substrate to a desiredy-axis and z-axis location to facilitate performing certain processingon the substrate.

[0009] In another aspect, the processing performed on the substrateinvolves ion implantation. A chamber is provided into which an ion beamis entered, the ion beam configured to scan over the width of asubstrate along an x-axis. Within the chamber is the linkage attached ata first rotary axis to the base and the end effector member attached ata second rotary axis to the linkage, the linkage and end effector memberforming a substrate holder to position the substrate. A drive unit ismechanically connected to the linkage to scan the end effector and heldsubstrate through the ion beam substantially in a z-axis direction.Because the end effector member rotates about the second rotary axis asthe linkage rotates about the first rotary axis, a substantiallyconstant angle of incidence of the ion beam on the substrate ismaintained. The system can be further configured with the base beingmovable along the y-axis such that the system maintains a constantdistance of travel for the ion beam incident on the substrate as thelinkage and end effector member travel in a curved path.

[0010] Other advantages and components of the present invention willbecome apparent from the following description taken in conjunction withthe accompanying drawings, which constitute a part of this specificationand wherein are set forth exemplary aspects of the present invention toillustrate various features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view an embodiment of the presentinvention showing a substrate mounted to the end effector member.

[0012]FIG. 2 is a side elevation view of the present invention accordingto the embodiment of FIG. 1.

[0013]FIG. 3 is a perspective view of another embodiment of the presentinvention showing the base being movable along a linear slide.

[0014]FIG. 4 is a side elevational view of the present inventionaccording to the embodiment of FIG.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The substrate positioning system 10 of the present invention isshown generally in FIGS. 1 and 2. The system 10 provides a linkage 12rotatably mounted to a base 14 with a first rotary joint 16 at a firstrotary axis 18 and an end effector member 20 rotatably mounted to thelinkage 12 with a second rotary joint 22 at a second rotary axis 24 forproperly positioning a substrate 26 for various processing. The firstrotary axis 18 is located at a proximal end 28 of the linkage 12 and thesecond rotary axis 24 is located at a distal end 30 of the linkage 12.Both axes are aligned in parallel relationship to one another and extendgenerally parallel to the x-axis. Thus, the base 14 extends upward alongthe z-axis and the linkage 12 and end effector member 20 generally movein the y-z plane. Through the synchronized rotation of the linkage 12about the base 14 and the end effector member 20 about the linkage 12,the system 10 acts as a robotic unit to move the substrate 26 to thedesired location, through a known path at desired velocity.

[0016] The rotation of the linkage 12 and end effector member 20 aboutthe first and second rotary axes 18, 24, respectively, can beaccomplished by various means. The linkage 12 and end effector member 20may be mechanically coupled using suitable linkages such as belts andpulleys (not shown), or may be independently controlled through motors(not shown) coupled to each of the linkage and the member. If motors areused, they are preferably mounted within the first and second rotaryjoints 16, 22. The linkage 12 is thus extended or contracted relative tothe base 14 and the end effector member 20 is extended or contractedrelative to the linkage 12. The motion of the linkage 12 and member 20is in the y-z plane.

[0017] Although the system 10 can be used in a variety of ways,preferably, the substrate 26 is fixedly positioned on the end effectormember 20 such that the system 10 moves the substrate through an ionbeam for performing ion implantation. In this aspect, the end effectormember 20 has a planar surface 32 upon which the substrate 26, such as asemiconducting wafer, is mounted. The surface 32 is alignedperpendicular to the length of the member 20 extending from the secondrotary axis 24 to the surface 32, as best seen in FIG. 2. The linkage 12is an elongate member having a length sufficient as to move the endeffector member 20 and wafers 26 of various sizes vertically though theion beam path. Mounting of the wafer 26 to the surface 32 is preferablyaccomplished by clamping the wafer thereon. Also, the wafer 26 isgenerally of the type with a surface area in the form of a disk with adiameter and center.

[0018] As seen in FIG. 2, the system 10 is contained within an evacuatedenclosure 34 such that an environment conductive to ion beam transportand implantation is provided. The ion beam is introduced into theenclosure 34 from the end of an ion beam transport system 36, which ispreferably at a fixed location and transmits the beam along the y-axistowards the wafer 26. As is known in the art, the ion beam iselectronically scanned across the held wafer 26 along an axis (thex-axis) or in a fan shaped orientation. This provides an ion beamincident on the wafer 26 that is formed as an elongated shape to deliveruniform ion dosage across the width of the wafer in the x-axis, but doesnot provide an ion beam substantially across the wafer height,perpendicular to the x-axis. The movement of the end effector member 20mechanically scans the wafer 26 through the ion beam along an axisperpendicular to the electronically scanned ion beam such that an entirewafer surface 38 may be uniformly ion implanted. The velocities of themechanical scan preferably move the wafer 26 through the ion beam on theorder of at least 10 inches per second.

[0019] To ensure that the proper ion dosage is applied to the wafer 26,the planar surface 32 of the end effector member 20 is maintained at aconstant angle of incidence, or implant angle, with the ion beamthroughout the mechanical scan. The implant angle can be set at anyangle between 0 and 90 degrees depending on the desired ion dosagecharacteristics. This is accomplished by the coordination of therotation of the linkage 12 and end effector member 20. Because therotation of the linkage 12 about the first rotary axis 18 causes thelinkage distal end 30 to rotate, the second rotary axis 24 mustsimultaneously counter-rotate in a synchronous fashion to ensure thatthe end effector member 20 and surface 32 upon which the wafer 26 isaffixed remain properly oriented at the chosen implant angle. The firstand second rotary axes 18, 24 are coordinated to rotate in oppositedirections (clockwise and counter-clockwise) to properly orient the endeffector member 20. Further, the axes 18, 24 rotate with equal butopposite angular magnitude, or degree of rotation, to maintain theconstant implant angle. Motors, belts and pulleys, or other means areimplemented to rotate the linkage 12 and end effector member 20 aboutthe axes 18, 24. Also, logic circuits and/or processors may beelectrically connected to the means for rotating the linkage 12 andmember 20 to accomplish the programmed coordination of the rotation.Additionally, other factors such as the mechanical scan velocity, theion beam current, or the duty cycle of the electronic scan, may beindividually or simultaneously adjusted to provide the proper iondosage.

[0020] The vertical component of the mechanical scanning is accomplishedthrough the rotation of the linkage 12 about the base 14, which is astructure with a fixed position relative to the z-axis. The wafer 26 maybe moved several times through the ion beam such that all portions ofthe wafer surface 38 receive the adequate ion beam dosage. The functionof the end effector member 20 is thus to provide a secure platform forthe wafer 26 for orientation at the desired implant angle throughoutthese scans.

[0021] In another aspect shown in FIGS. 3 and 4, the base 14 of thesystem 10 may be provided with a means for linearly moving the base 40such that the horizontal distance along the y-axis between the ion beamtransport system end 36 and the impact point 42 of the beam on the wafersurface 38 remains constant throughout the mechanical scan. Preferably,the means 40 for moving the base 14 is a linear slide that moves withina track 44. Because rotation of the linkage 12 about the base 14 causesthe linkage distal end 30 and end effector member 20 mounted thereto tofollow a curved path, the wafer surface 38 moves both vertically alongthe z-axis and horizontally along the y-axis. The movement of the linearslide 40 allows the base 14, and thus the linkage 12 and member 20coupled thereto, to counteract the y-axis component of the holder 20rotation and facilitate the translation of the impact point 42 on thewafer surface 38 moving substantially only in the z-axis. The intensityof the ion beam reaching the wafer surface 38 is maintained as thesurface is moved through the beam.

[0022] Assuming that the wafer 26 is affixed to the substrate surface 32such that the wafer surface 38 is orthogonal to the end effector member20 length and the ion beam travels in a parallel line with the y-axis,the formula for calculating the necessary linear movement of the base14, or correction factor, can be calculated. First, the necessary beamtravel distance from the ion beam transport system end 36 to the impactpoint 42 on the wafer surface is determined. The base 14 is moved suchthat the wafer 26 is properly positioned for the necessary beam travel.A correction factor K is determined by the difference of a constant E₁,which is the y-axis distance from the first rotary axis 18 to the beamimpact point 42 on the wafer surface 38 at the starting point of the ionscan, and the y-axis distance E from the first rotary axis 18 of thebase to the beam impact point 42 on the wafer surface 38 as the linkage12 and end effector member 20 are rotated. Thus, the correction factor Kis calculated as:

K=E1−E;

[0023] wherein: K is a positive value when the ion beam impact point 42has moved further from the ion beam transport system end 36 and anegative positive value when the beam impact point has moved closer tothe beam output location.

[0024] If the linkage 12 and the end effector member 20 extend parallelto the y-axis, the distance E is determined to be:

E=A+B;

[0025] wherein: A is the length of the end effector member 20 from thesecond rotary axis 24 to the substrate 26 affixed thereto, plus thethickness of the substrate; and B is the length of the linkage 12 fromthe first rotary axis 18 to the second rotary axis.

[0026] When the linkage 12 and end effector member 20 are rotated aboutthe first and second rotary axes, 18, 24, respectively, to move thesubstrate 26 through the ion beam, the cosine of the angles formed withthe y-axis must be determined. Thus, for an implant angle of 0 degrees,the distance E is determined by:

E=A(cos Γ)+B(cos θ);

[0027] wherein: θ is the angle between the linkage 12 and the y-axis atthe first rotary axis 18, positively measured above the z-axis; and Γ isangle between the end effector member 20 and the y-axis at the secondrotary axis 24, positively measured above the y-axis. However, because ris equal to the implant angle (because the wafer surface is orthogonalto the end effector length), the value of Γ is zero and the equationreduces to:

E=A+B(cos θ).

[0028] The correction factor is then calculated to be:

K=E1−(A+B(cos θ)).

[0029] The determination of the correction factor changes when animplant angle of greater than zero but less than 90 degrees isintroduced. The distance E must not only take into account therelationship between the cosine of the angles formed between the linkage12 and end effector member 20 with the y-axis, but also the z-axisposition the ion beam impacts the wafer surface 38. To offset from theposition of the wafer 26 at the centerline 44 of the end effector lengthto the beam impact point 42, the following relationship is observed:

tan (α)=G/F or G=F·tan (α);

[0030] wherein: α is the implant angle between the wafer surface 38 andthe z-axis measured at the ion beam impact point 42; F is the z-axisdistance from the wafer surface 38 at the centerline of the end effectorlength 44 to the beam impact point; and G is the y-axis distance fromthe wafer surface at the centerline of the end effector length to thebeam impact point. Thus, knowing the implant angle α and the distance F,the distance G can be determined and added to the cosine of the linkageand end effector member angles to determine E. The distance F iscalculated from:

F=C+B(sin θ)+A(sin θ)−D;

[0031] Wherein: C is the z-axis distance from a reference x-yplane uponwhich the base 14 is positioned to the first rotary axis 18; and D isthe z-axis distance from the reference x-yplane to the ion beamtransport system end 36. The distance E is calculated from:

E=A(cos Γ)+B(cos θ)+G;

[0032] Therefore, E is determined to be:

E=A(cos Γ)+B(cos θ)+tan (α)·[A(sin Γ)+B(sin θ)+C−D];

[0033] and the correction factor is then calculated to be:

K=E1−A(cos Γ)+B(cos θ)+tan(α)·[A(sin Γ)+B(sin θ)+C−D].

[0034] Knowing the correction factor, logic circuits and/or processorsmay be electrically connected to the means 40 for linearly moving thebase 14 in a y-axis direction such that the base is linearly moved basedon the calculated correction factor to thereby maintain a constanttravel distance for the ion beam from an ion beam transport system end36 to ion beam impact point 42 on the substrate surface 38.

[0035] From the foregoing information, it should now be obvious that thesubstrate positioning system 10 provides a simple and efficient solutionfor accurately positioning a substrate to facilitate the performing ofcertain processing on the substrate, such as ion implantation. Thesystem is ideally configured to move the substrate vertically along az-axis through an ion beam scan while reducing or eliminating y-axishorizontal motion of an ion beam impact location on the held substrate.In this way, the proper amount of ion beam dosage is delivered evenlyover the surface of the substrate. It is also to be understood that thethat terms used herein relating to vertical dimensions along the z-axisand horizontal dimensions along the yaxis are relative, and the systemcan be rotated in any of the x, y, or z axes such that vertical andhorizontal orientations would be changed accordingly. While certainforms of the present invention have been illustrated and describedherein, it is not to be limited to the specific forms or arrangement ofparts described and shown.

What is claimed is:
 1. A substrate positioning system, comprising: alinkage rotatably mounted on a first rotary axis to a base, the baseextending above an x-y reference plane; an end effector member rotatablymounted on a second rotary axis to a mounting portion of the linkage,the end effector member configured for supporting a substrate thereto;and means for rotating the linkage about the first rotary axis; whereinthe rotation of the linkage about the first axis causes movement of themounting portion of the linkage and substantially positions the endeffector member and substrate at a specific y-axis and z-axis locationto facilitate processing on the substrate.
 2. The positioning system ofclaim 1, wherein a means for performing processing on the substrate ispositioned at a fixed location relative to the x-y reference plane. 3.The positioning system of claim 1, wherein the rotating means ismechanically connected to the linkage.
 4. The positioning system ofclaim 1, wherein the end effector member is positioned as to maintain aconstant angle between a surface of the substrate and the z-axis.
 5. Thepositioning system of claim 4, wherein the first rotary axis isconfigured to rotate in a direction opposite of the second rotary axisas to maintain a constant angle between a surface of the substrate andthe z-axis.
 6. The positioning system of claim 5, wherein the firstrotary axis is configured to rotate with the same angular magnitude asthe second rotary axis.
 7. The positioning system of claim 1, whereinthe linkage has a proximal end and a distal end, the linkage beingmounted to the base at the proximal end and the end effector memberbeing mounted to the distal end.
 8. The positioning system of claim 1,wherein the means for rotating the linkage is further mechanicallyconnected to the end effector member to rotate the end effector memberabout the second rotary axis and thereby position the end effectormember and the substrate at a specific y-axis and z-axis location forperforming processing on the substrate.
 9. The positioning system ofclaim 8, wherein the means for rotating the linkage is configured tomaintain a constant angle between a surface of the substrate and thez-axis.
 10. The positioning system of claim 1, further comprising asecond means mechanically connected to the end effector member to rotatethe member about the second rotary axis to position the member and thesubstrate at a specific y-axis and zaxis location for performingprocessing on the substrate.
 11. The positioning system of claim 10,wherein the second means for rotating the end effector member isconfigured to maintain a constant angle between a surface of thesubstrate and the z-axis.
 12. The positioning system of claim 1, whereinthe means for rotating the linkage comprises a motor.
 13. Thepositioning system of claim 1, wherein the processing performed on thesubstrate comprises ion implantation by scanning the substrate with anion beam travelling generally in a y-axis plane.
 14. The positioningsystem of claim 13, wherein the substrate is a semiconducting wafer. 15.The positioning system of claim 13, further comprising a means forlinearly moving the base in a y-axis direction to maintain a constanttravel distance for the ion beam from an ion beam transport system endto an impact point of the beam with the substrate while the linkage isbeing rotated to position the substrate at a specific z-axis location.16. The positioning system of claim 15, wherein the end effector memberis positioned as to maintain a constant implant angle for the ion beamwith a surface of the substrate, and the movement of the base tomaintain a constant travel distance for the ion beam is determined bythe equation or the relation substantially equivalent thereto: K=E1A(cosΓ)+B(cos θ)+tan (α)·(A(sin Γ)+B(sin θ)+C−D), wherein K: a correctionfactor to determine the linear distance of travel of the base necessaryto maintain a constant travel distance for the ion beam, E1: a constanty-axis distance measured from the first rotary axis of the base to theion beam impact point on the substrate when the substrate is positionedat the desired distance from ion beam output location, the first rotaryaxis being an x-axis, A: a length of the end effector member from thesecond rotary axis to the substrate affixed thereto plus the thicknessof the substrate, the second rotary axis being an x-axis, B: length ofthe linkage from the first rotary axis of the base to the second rotaryaxis, the first rotary axis being an x-axis, C: a z-axis distance from areference x-y plane upon which the base is positioned to the firstrotary axis, D: a z-axis distance from the reference x-y plane to theion beam output location, θ: an angle between the linkage and the z-axisat the first rotary axis, positively measured above the z-axis, Γ: anangle between the end effector member and the z-axis at the secondrotary axis, positively measured above the z-axis, and α: an ion implantangle between the substrate surface and the z-axis measured at the ionbeam impact point and having a fixed value between 0 and 90 degrees. 17.An ion implantation apparatus, comprising: a chamber into which an ionbeam is entered, the ion beam being configured for scanning over thewidth of a substrate along an x-axis, the substrate being positioned inthe chamber; a substrate holder comprising a linkage and an end effectormember, the linkage having a proximal end with a first rotary axis and adistal end with a second rotary axis, the first rotary axis attached toa base and the second rotary axis attached to the end effector member,the substrate holder positioning the substrate in the chamber; and adrive unit mechanically connected to the linkage to move the substratethrough the ion beam substantially in a direction along a z-axisperpendicular to the direction of the ion beam scan; wherein the endeffector member is configured to rotate about the second rotary axis asthe linkage rotates about the first rotary axis to maintain asubstantially constant implant angle of the substrate relative to theion beam.
 18. The positioning system of claim 17, wherein the ion beamis configured to travel generally along a y-axis.
 19. The apparatus ofclaim 18, wherein variations of the dose of the ion beam reaching thesubstrate, caused by the changing distance the ion beam has to travelalong the y-axis to reach the substrate due to the rotation of the endeffector member, are avoided by calculating a correction factor andadjusting at least one of the ion beam current, the duty cycle of theion beam scan, and the mechanical scan velocity to produce a constantdose of the ion beam.
 20. The apparatus of claim 17, wherein the firstand second rotary axes are parallel to the x-axis.
 21. The apparatus ofclaim 17, wherein the first rotary axis is configured to rotate in adirection opposite of the second rotary axis as to maintain thesubstantially constant implant angle.
 22. The apparatus of claim 21,wherein the first rotary axis is configured to rotate with the sameangular magnitude as the second rotary axis.
 23. The apparatus of claim17, wherein the drive unit is further mechanically connected to the endeffector member to aid in moving the substrate through the ion beamsubstantially in a direction along a z-axis perpendicular to thedirection of the ion beam scan.
 24. The apparatus of claim 17, furthercomprising an end effector drive unit mechanically connected to the endeffector member to move the substrate through the ion beam substantiallyin a direction along a z-axis perpendicular to the direction of the ionbeam scan.
 25. The positioning system of claim 17, wherein the substrateis a semiconducting wafer.
 26. The positioning system of claim 18,further comprising a means for linearly moving the base in a y-axisdirection to maintain a constant travel distance for the ion beam froman ion beam transport system end to an impact point of the beam with thesubstrate while the substrate holder is being rotated to move thesubstrate through the ion beam more precisely in a direction along thez-axis.
 27. The positioning system of claim 26, wherein the substrate isaffixed to the end effector member, and the movement of the base tomaintain a constant travel distance for the ion beam is determined bythe equation or the relation substantially equivalent thereto:K=E1−A(cos Γ)+B(cos θ)+tan (α)·(A(sin Γ)+B(sin θ)+C−D), wherein K: acorrection factor to determine the linear distance of travel of the basenecessary to maintain a constant travel distance for the ion beam, E1: aconstant y-axis distance measured from the first rotary axis of the baseto the ion beam impact point on the substrate when the substrate ispositioned at the desired distance from ion beam output location, thefirst rotary axis being an x-axis, A: a length of the end effectormember from the second rotary axis to the substrate affixed thereto plusthe thickness of the substrate, B: length of the linkage from the firstrotary axis to the second rotary axis, C: a z-axis distance from areference x-y plane upon which the base is positioned to the firstrotary axis, D: a z-axis distance from the reference x-y plane to theion beam output location, θ: an angle between the linkage and the z-axisat the first rotary axis, positively measured above the z-axis, Γ: anangle between the end effector member and the z-axis at the secondrotary axis, positively measured above the z-axis, and α: an ion implantangle between a substrate surface and the z-axis measured at the ionbeam impact point and having a fixed value between 0 and 90 degrees. 28.A method for ion implantantion on a substrate, comprising the steps of:positioning a substrate on a substrate holder, the holder comprising alinkage and an end effector member, the linkage having a proximal endwith a first rotary axis and a distal end with a second rotary axis, thefirst rotary axis attached to a base and the second rotary axis attachedto the end effector member, the holder being disposed within a chamberinto which an ion beam is entered, the ion beam being configured forscanning over the width of the substrate along an x-axis; andtranslating the substrate through the ion beam substantially in adirection along a z-axis perpendicular to the direction of the ion beamscan by simultaneously rotating the linkage at the first rotary axisabout the base and rotating the end effector member at the second rotaryaxis about the linkage so as to maintain a substantially constantimplant angle of the substrate relative to the ion beam.
 29. The methodof claim 28, further comprising moving the base linearly in a y-axisdirection to maintain a constant travel distance for the ion beam froman ion beam transport system end to an impact point of the beam with thesubstrate while the substrate holder is being rotated to move thesubstrate through the ion beam more precisely in a direction along thez-axis.
 30. The method of claim 28, wherein the movement of the base tomaintain a constant travel distance for the ion beam is determined bythe equation or the relation substantially equivalent thereto:K=E1−A(cos Γ)+B(cos θ)+tan (α)·(A(sin Γ)+B(sin θ)+C−D), wherein K: acorrection factor to determine the linear distance of travel of the basenecessary to maintain a constant travel distance for the ion beam, E1: aconstant y-axis distance measured from the first rotary axis of the baseto the ion beam impact point on the substrate when the substrate ispositioned at the desired distance from ion beam output location, thefirst rotary axis being an x-axis, A: a length of the end effectormember from the second rotary axis to the substrate affixed thereto plusthe thickness of the substrate, B: length of the linkage from the firstrotary axis to the second rotary axis, C: a z-axis distance from areference x-y plane upon which the base is positioned to the firstrotary axis, D: a z-axis distance from the reference x-y plane to theion beam output location, θ: an angle between the linkage and the z-axisat the first rotary axis, positively measured above the z-axis, Γ: anangle between the end effector member and the z-axis at the secondrotary axis, positively measured above the z-axis, and α: an ion implantangle between a substrate surface and the z-axis measured at the ionbeam impact point and having a fixed value between 0 and 90 degrees. 31.The method of claim 28, wherein the substrate is a semiconducting wafer.